Authors: Brown, IR; Wood, PJ

Open access courtesy of:


Cite As:
Brown, IR & Wood, PJ 2023, 'The case for using three-dimensional limit equilibrium stability analysis', in PM Dight (ed.), SSIM 2023: Third International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, pp. 927-938,

Download citation as:   ris   bibtex   endnote   text   Zotero

At the previous Slope Stability in Mining conference, in 2021, Dr John Read claimed that there are geological and mathematical uncertainties in the method used for 3D limit equilibrium (LE) stability analyses. We acknowledge the valid issues raised by Dr Read, and our paper explains how we have developed a software system that provides a reliable 3D LE analysis for slopes in complex geology. Our experience with developing 3D LE software (TSLOPE) began in 1989 when we were able to show that the 3D LE analysis of the stability of a proposed canyon landfill in Southern California gave a much higher Factor of Safety than that calculated for a 2D section along the axis of the canyon. We have discarded many of the methods used in 2D LE software packages as they do not achieve full force and moment equilibrium and are a relic from a time when we were limited by computational ability. Our paper discusses the background and underlying theory supporting our 3D LE software and provides comparisons of 3D and 2D analyses carried out using the same geological model.

Keywords: slope stability, 3D, limit equilibrium, Spencer’s method, TSLOPE

Cheng, YM & Yip, CJ 2007, ‘Three-dimensional asymmetrical slope stability analysis extension of Bishop’s, Janbu’s and Morgenstern-Price’s techniques’, Journal of Geotechnical and Geoenvironmental Engineering vol. 133, no. 12, pp.1544–1555.
Gillon, MD, Graham, CJ & Grocott, GG 1992, ‘Low level drainage works at the Brewery Creek Slide, in DH Bell (ed.), Proceedings of the Sixth International Symposium on Landslides, A.A. Balkema, Rotterdam, pp. 715–720.
Read, JRL 2021, ‘Three-dimensional limit equilibrium slope stability analyses, method, and design acceptance criteria uncertainties’, in PM Dight (ed.), SSIM 2021: Second International Slope Stability in Mining, Australian Centre for Geomechanics, Perth,
pp. 3–10,
Spencer, E 1967, ‘A method of analysis of the stability of embankments assuming parallel inter-slice forces’, Géotechnique, vol. 17, no. 1, pp. 11–26.
TAGAsoft 2023, TSLOPE, version 2.3, computer software, TAGA Engineering Software Ltd, Wellington,
TECHBASE International, Ltd 2007, TECHBASE® Reference Manual, TECHBASE International, Ltd, Reno.
Wyllie, DC 2017, Rock Slope Engineering, CRC Press, Boca Raton.

© Copyright 2024, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
View copyright/legal information
Please direct any queries or error reports to